linux-kernel - [PATCH] drm/amd/display: avoid passing enum as NULL pointer

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Date:   Thu,  7 Mar 2019 11:34:29 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Harry Wentland <harry.wentland@....com>,
        Leo Li <sunpeng.li@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "David (ChunMing) Zhou" <David1.Zhou@....com>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Arnd Bergmann <arnd@...db.de>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Anthony Koo <Anthony.Koo@....com>, Aric Cyr <Aric.Cyr@....com>,
        Harmanprit Tatla <Harmanprit.Tatla@....com>,
        Ken Chalmers <ken.chalmers@....com>,
        SivapiriyanKumarasamy <sivapiriyan.kumarasamy@....com>,
        Kees Cook <keescook@...omium.org>,
        Bayan Zabihiyan <Bayan.Zabihiyan@....com>,
        Tony Cheng <Tony.Cheng@....com>, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: [PATCH] drm/amd/display: avoid passing enum as NULL pointer

The mod_freesync_build_vrr_infopacket() function uses rather obscure
calling conventions, where an enum is passed in through a pointer,
and a NULL pointer is expected to behave the same way as the zero-value
(TRANSFER_FUNC_UNKNOWN).

Trying to build this with clang results in a warning:

drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm.c:4601:3: error: expression which evaluates to zero treated
      as a null pointer constant of type 'const enum color_transfer_func *' [-Werror,-Wnon-literal-null-conversion]

Passing it by value instead of by reference makes the code simpler
and more conventional but should not change the behavior at all.

Fixes: c2791297013e ("drm/amd/display: Add color bit info to freesync infoframe")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/gpu/drm/amd/display/modules/freesync/freesync.c | 7 +++----
 drivers/gpu/drm/amd/display/modules/inc/mod_freesync.h  | 2 +-
 2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/modules/freesync/freesync.c b/drivers/gpu/drm/amd/display/modules/freesync/freesync.c
index 94a84bc57c7a..6f32fe129880 100644
--- a/drivers/gpu/drm/amd/display/modules/freesync/freesync.c
+++ b/drivers/gpu/drm/amd/display/modules/freesync/freesync.c
@@ -724,7 +724,7 @@ static void build_vrr_infopacket_v1(enum signal_type signal,
 
 static void build_vrr_infopacket_v2(enum signal_type signal,
 		const struct mod_vrr_params *vrr,
-		const enum color_transfer_func *app_tf,
+		const enum color_transfer_func app_tf,
 		struct dc_info_packet *infopacket)
 {
 	unsigned int payload_size = 0;
@@ -732,8 +732,7 @@ static void build_vrr_infopacket_v2(enum signal_type signal,
 	build_vrr_infopacket_header_v2(signal, infopacket, &payload_size);
 	build_vrr_infopacket_data(vrr, infopacket);
 
-	if (app_tf != NULL)
-		build_vrr_infopacket_fs2_data(*app_tf, infopacket);
+	build_vrr_infopacket_fs2_data(app_tf, infopacket);
 
 	build_vrr_infopacket_checksum(&payload_size, infopacket);
 
@@ -757,7 +756,7 @@ void mod_freesync_build_vrr_infopacket(struct mod_freesync *mod_freesync,
 		const struct dc_stream_state *stream,
 		const struct mod_vrr_params *vrr,
 		enum vrr_packet_type packet_type,
-		const enum color_transfer_func *app_tf,
+		const enum color_transfer_func app_tf,
 		struct dc_info_packet *infopacket)
 {
 	/* SPD info packet for FreeSync
diff --git a/drivers/gpu/drm/amd/display/modules/inc/mod_freesync.h b/drivers/gpu/drm/amd/display/modules/inc/mod_freesync.h
index 4222e403b151..645793b924cf 100644
--- a/drivers/gpu/drm/amd/display/modules/inc/mod_freesync.h
+++ b/drivers/gpu/drm/amd/display/modules/inc/mod_freesync.h
@@ -145,7 +145,7 @@ void mod_freesync_build_vrr_infopacket(struct mod_freesync *mod_freesync,
 		const struct dc_stream_state *stream,
 		const struct mod_vrr_params *vrr,
 		enum vrr_packet_type packet_type,
-		const enum color_transfer_func *app_tf,
+		const enum color_transfer_func app_tf,
 		struct dc_info_packet *infopacket);
 
 void mod_freesync_build_vrr_params(struct mod_freesync *mod_freesync,
-- 
2.20.0